1996 slx 780 no power in the water. top end just rebuilt

my 1996 slx 780 I just replace the cylinders and pistons I had a oil line come off and I scored a cylinder. I engine starts rightup out of the water. I put it in the water and I can not even get it to idle. I tried giving gas and it stalls out.
The MFD is displaying LOPRS not sure what that means.
Before the cylinder got scored the engine ran good.

Depending on how long you ran the engine with the oil line off, it's entirely possible you have deeper troubles. Lack of lubrication can tear up the bearings in a hurry. You could have deep crank troubles.

Just curious, but how would lower compression on 1 cyl mean a possible bad bearing?

To check crank and wrist pin bearings though: You need to remove all the spark plugs and engine coupler. Then rotate the crank by hand listen/feel for any tightness, gritiness, or anything out of the ordinary. Twist it in both directions. Remember that the magnets on the flywheel are going to give you some resitance, and that's normal.